3,369 research outputs found
Spherical Formulation for Diagramatic Evaluations on a Manifold with Boundary
The mathematical formalism necessary for the diagramatic evaluation of
quantum corrections to a conformally invariant field theory for a
self-interacting scalar field on a curved manifold with boundary is considered.
The evaluation of quantum corrections to the effective action past one-loop
necessitates diagramatic techniques. Diagramatic evaluations and higher
loop-order renormalisation can be best accomplished on a Riemannian manifold of
constant curvature accommodating a boundary of constant extrinsic curvature. In
such a context the stated evaluations can be accomplished through a consistent
interpretation of the Feynman rules within the spherical formulation of the
theory for which the method of images allows. To this effect, the mathematical
consequences of such an interpretation are analyzed and the spherical
formulation of the Feynman rules on the bounded manifold is, as a result,
developed.Comment: 12 pages, references added. To appear in Classical and Quantum
Gravit
Genealogies of rapidly adapting populations
The genetic diversity of a species is shaped by its recent evolutionary
history and can be used to infer demographic events or selective sweeps. Most
inference methods are based on the null hypothesis that natural selection is a
weak or infrequent evolutionary force. However, many species, particularly
pathogens, are under continuous pressure to adapt in response to changing
environments. A statistical framework for inference from diversity data of such
populations is currently lacking. Toward this goal, we explore the properties
of genealogies in a model of continual adaptation in asexual populations. We
show that lineages trace back to a small pool of highly fit ancestors, in which
almost simultaneous coalescence of more than two lineages frequently occurs.
While such multiple mergers are unlikely under the neutral coalescent, they
create a unique genetic footprint in adapting populations. The site frequency
spectrum of derived neutral alleles, for example, is non-monotonic and has a
peak at high frequencies, whereas Tajima's D becomes more and more negative
with increasing sample size. Since multiple merger coalescents emerge in many
models of rapid adaptation, we argue that they should be considered as a
null-model for adapting populations.Comment: to appear in PNA
Renormalisation of the Nonperturbative Thermal Pressure
We show how the fully resummed thermal pressure is rendered ultraviolet
finite by standard zero-temperature renormalisation. The analysis is developed
in a 6-dimensional scalar model that mimics QED and has flavours. The
limit of the model can be calculated completely. At a critical
temperature, one of the degrees of freedom has vanishing screening mass like
the transverse gauge bosons in four-dimensional finite-temperature perturbation
theory. The renormalised nonperturbative interaction pressure of this model is
evaluated numerically.Comment: 27 pages, plain tex, with 10 figures embedded using eps
From Correlators to Wilson Loops in Chern-Simons Matter Theories
We study n-point correlation functions for chiral primary operators in three
dimensional supersymmetric Chern-Simons matter theories. Our analysis is
carried on in N=2 superspace and covers N=2,3 supersymmetric CFT's, the N=6
ABJM and the N=8 BLG models. In the limit where the positions of adjacent
operators become light-like, we find that the one-loop n-point correlator
divided by its tree level expression coincides with a light-like n-polygon
Wilson loop. Remarkably, the result can be simply expressed as a linear
combination of five dimensional two-mass easy boxes. We manage to evaluate the
integrals analytically and find a vanishing result, in agreement with previous
findings for Wilson loops.Comment: 32 pages, 6 figures, JHEP
Thermodynamics of the \phi^4 theory in tadpole approximation
Relying on the Luttinger-Ward theorem we derive a thermodynamically
selfconsistent and scale independent approximation of the thermodynamic
potential for the scalar theory in the tadpole approximation. The
resulting thermodynamic potential as a function of the temperature is similar
to the one of the recently proposed screened perturbation theory.Comment: 6 pages, including 1 eps figur
Low temperature relations in QCD
In this talk I discuss the low temperature relations for the trace of the
energy-momentum tensor in QCD with two and three quarks. It is shown that the
temperature derivatives of the anomalous and normal (quark massive term)
contributions to the trace of the energy-momentum tensor in QCD are equal to
each other in the low temperature region. Leading corrections connected with
-interactions and thermal excitations of and mesons are
calculated.Comment: 10 pages, LaTeX2e. Talk given at 12th International Seminar on
High-Energy Physics (QUARKS 2002), Novgorod, Russia, 1-7 Jun 200
Kappa-symmetric Derivative Corrections to D-brane Dynamics
We show how the superembedding formalism can be applied to construct
manifestly kappa-symmetric higher derivative corrections for the D9-brane. We
also show that all correction terms appear at even powers of the fundamental
length scale . We explicitly construct the first potential correction, which
corresponds to the kappa-symmetric version of the , which one
finds from the four-point amplitude of the open superstring.Comment: 20 pages. Minor changes, added reference
Comments on gluon scattering amplitudes via AdS/CFT
In this article we consider n gluon color ordered, planar amplitudes in N=4
super Yang Mills at strong 't Hooft coupling. These amplitudes are approximated
by classical surfaces in AdS_5 space. We compute the value of the amplitude for
a particular kinematic configuration for a large number of gluons and find that
the result disagrees with a recent guess for the exact value of the amplitude.
Our results are still compatible with a possible relation between amplitudes
and Wilson loops.
In addition, we also give a prescription for computing processes involving
local operators and asymptotic states with a fixed number of gluons. As a
byproduct, we also obtain a string theory prescription for computing the dual
of the ordinary Wilson loop, Tr P exp[ i\oint A ], with no couplings to the
scalars. We also evaluate the quark-antiquark potential at two loops.Comment: 27 pages, 9 figures,v3:minor correction
Perturbation theory vs. simulation for tadpole improvement factors in pure gauge theories
We calculate the mean link in Landau gauge for Wilson and improved SU(3)
anisotropic gauge actions, using two loop perturbation theory and Monte Carlo
simulation employing an accelerated Langevin algorithm. Twisted boundary
conditions are employed, with a twist in all four lattice directions
considerably improving the (Fourier accelerated) convergence to an improved
lattice Landau gauge. Two loop perturbation theory is seen to predict the mean
link extremely well even into the region of commonly simulated gauge couplings
and so can be used remove the need for numerical tuning of self-consistent
tadpole improvement factors. A three loop perturbative coefficient is inferred
from the simulations and is found to be small. We show that finite size effects
are small and argue likewise for (lattice) Gribov copies and double Dirac
sheets.Comment: 13 pages of revtex
Planar quark scattering at strong coupling and universality
We discuss scattering of fundamental matter in the planar and strong coupling
limit via the AdS/CFT correspondence, generalizing the recently proposed
calculation for adjoint matter due to Alday and Maldacena [arXiv:0705.0303].
Color decomposition of quark amplitudes is a key property allowing to repeat
the procedure in the case of fundamental matter and to derive the relation of
these strong coupling amplitudes to minimal area problems. We present the
results for two different D3-D7 systems, one is only conformal in the planar
limit and the other is exactly conformal. Our results suggest a universal
behavior of scattering amplitudes at strong coupling and planar limit (both for
gluons and quarks).Comment: 13 pages, 4 figures, JHEP format. v2: added references and minor
corrections. v3: following arXiv:0710.0393 we change our claim about a
minimal surface solution without spike singularities. We make the appropriate
corrections where necessar
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